What is the ruling on the the graduation cap, and is it forbidden to imitate the disbelievers in everything they wear or make?

The criterion for prohibited imitation (tashabbuh) is that the act is exclusive to disbelievers or transgressors, or has become a distinctive symbol for them. If it becomes widespread among Muslims and is no longer distinctive to disbelievers, then it ceases to be a prohibited imitation, unless it is prohibited for another reason. Based on this, the ruling on the graduation cap – whether it is prohibited – is determined by considering the extent to which it is exclusive to disbelievers or transgressors. As for modern devices, they are permissible and do not constitute imitation. Indeed, the Prophet, peace and blessings be upon him, adopted the trench (khandaq) from the Persians, and 'Umar also adopted the administrative registers (dawawin) from the Persians.